Fusion Science and Technology / Volume 47 / Number 1T / January 2005 / Pages 309-311
Technical Paper / Open Magnetic Systems for Plasma Confinement
A diagnostic beam system has been developed for the GDT. This injector is the modification of the diagnostic injector RFX-DNBI. The system is primarily used for magnetic field measurements via motional Stark effect (MSE). The ion source provides 50keV, 5A hydrogen beam. Ions are extracted from a plasma created by an arc-discharge source and, after accelerating and focusing, are neutralized in a gas target. A plasma emitter, which is formed by collisionless expansion of a plasma jet on to the grids, has low perpendicular ion temperature. These results in rather low (0.01 rad) angular divergence of the extracted ion beam. In the accelerator, there is a set of four nested grids with 421 circular apertures of 4 mm diameter configured in a hexagonal pattern. The geometry of the elementary cell was optimized by using 2D computer code PBGUNS to obtain small angular divergence of the beam. The grids of ion optical system are spherically curved providing geometric focusing of the beam at a distance 1.5 m. Arc-discharge plasma box provides highly ionized plasma, so that the extracted beam has about 90% of full energy specie. The injector provides up to 4 ms duration pulse.